Instability Analysis of Mono Pile in Flexural and Buckling Modes Due to Liquefaction Induced Lateral Spreading-Paper

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The paper presents a simplified displacement-based framework for assessing the instability of mono piles in liquefiable soils. Unlike approaches that treat piles solely as columns and consider buckling, the framework models the pile as a beam-column and evaluates both buckling and flexural failure under axial loading and liquefaction-induced lateral spreading.<br /><br />The soil is represented by Winkler springs, with stiffness substantially reduced in liquefied layers. The model estimates pile response and critical axial load using buckling capacity and the pile section’s axial-load–moment interaction. Its predictions are compared with field observations from the Niigata Family Courthouse and show reasonable agreement, including the observed yielding near the boundary between liquefied and non-liquefied soil.<br /><br />A case study examines how lateral displacement and the depth of the non-liquefied surface crust affect pile performance. Greater lateral spreading reduces the critical axial load and increases susceptibility to flexural failure. With a significant non-liquefied crust, lateral soil drag can dominate, causing flexural failure and, in some cases, instability even without axial load. Under fully submerged conditions and small displacements, buckling may govern instead.<br /><br />The authors conclude that soil boundary conditions and the presence of a non-liquefied crust strongly influence the failure mode. The proposed framework offers a simplified tool for performance-based pile design in liquefiable soils, though it does not capture nonlinear soil behavior.

Keywords

mono piles

liquefiable soils

beam-column model

buckling capacity

flexural failure

Winkler springs

axial load-moment interaction

lateral spreading

pile instability

performance-based design